Modern nuclear radiation facilities, such as medical treatment and diagnostic facilities, require shielding structures to prevent leakage of radiation from the immediate site and origin of radiation to the surrounding environment. Generally, this shielding structure is constructed in the form of a room housing the source of radiation, whose walls comprise sufficiently dense materials at sufficiently deep thickness to insure blocking of radiation from escape to the outside of the room.
The most common method of constructing radiation-shielding structures involves pouring concrete walls, ceilings, and floors that can reach thicknesses of up to 10 feet. Higher-density varieties of concrete providing improved attenuation of gamma and neutron radiation exist, but they are difficult and expensive to pour in the same manner as traditional concrete. One method of utilizing this higher-density concrete material is to pre-fabricate blocks of cured concrete that can later be used to construct a shielding structure. The use of blocks permits reconfiguration of the shield for different experiments, and allows the shield to be disassembled for access to components located behind it. In addition, the shielding blocks are normally provided with a stepped offset to avoid direct line-of-sight radiation streaming, albeit with limited success, thereby necessitating the need for a plurality of wythes (i.e., multiple layers of complete walls). Due to inherently loose tolerances in concrete block formation, large gaps may result between adjacent blocks. In such cases, suitable radiation resistant material must be filled in these gaps. U.S. Pat. No. 4,437,013, for example, discloses such materials.
Conventional walls constructed using block generally employ mortar joints between blocks in each horizontal row or course, as well as between each course of blocks vertically layered on top of each other. Walls built with such mortared joints may yield an aesthetically pleasing, decorative appearance, revealing the block pattern, but they tend to be expensive, due at least in part to the cost of the mortar material and the labor cost involved in preparing and applying the mortar at the construction site. Such mortared construction is ordinarily performed by a skilled mason, thereby increasing the cost. Another disadvantage associated with mortared wall construction is that the joints are the weakest links in the structure. The concrete blocks themselves are typically crafted at a factory in a controlled environment, while mortar is applied under varying conditions on-site. In the end, block walls with relatively weak mortar joints are particularly susceptible to seismic damage.
Mortarless joint construction block systems offer an alternative to the labor intensive process used to prepare structures with mortar joints. These mortarless joint systems often rely on specific features that are formed on the blocks to interlock the blocks and hold the resulting wall together. In some cases the blocks may be designed for construction of walls comprising reinforced materials, such as re-bar, I-beams, and the like. U.S. Pat. No. 4,512,685 discloses examples of mortarless block wall construction. Reinforcement is commonly accomplished through voids designed in the blocks themselves, while the present invention may also include reinforcement by leaving gaps between blocks in a course. Such voids may thereafter be filled with mortar or other material, such as mortar, concrete, or other materials, including materials of like composition to the blocks.
Standard rectangular pre-formed concrete blocks are not suitable for use in radiation shielding structures because their layering in courses necessarily yields seams between blocks in a course, and between horizontally layered courses, which seams permit radiation to pass through the shielding structure. Additionally, multiple wythes are required in order to provide adequate shielding for the entire structure, thereby contributing to increased costs of materials and labor.
Other commonly used profile shapes, such as squares and triangles, also create seams between blocks that allow radiation to travel between the blocks relatively unattenuated. For example, U.S. Pat. Nos. 7,305,803, 4,107,894 and D377,397 disclose interlocking blocks capable of being constructed into walls, but all leave seams which do not block radiation. U.S. Pat. No. 4,035,975 discloses block with a variety of profiles, from triangular to curved, but all of its disclosed profiles yield seams with the same problem—the inability to block radiation. This is not altogether surprising in that the profiles used for interlocking blocks are shaped in such a way to provide only the ability for the blocks to interlock, without the appreciation (much less the solution) for eliminating radiation-passing seams. Additionally, the sharp angles of any such notched profiles are prone to breakage even with careful handling of the blocks when stacked on palettes for delivery to the construction site. Such breakage results in decreased locking-in of adjacent blocks, or even the inability to use such broken blocks, adding cost to construction.
Moreover, the curved profiles described in U.S. Pat. No. 4,035,975 provide for courses to be locked in one dimension only—side-to-side—providing no solution to forward backward mobility. Likewise, the profile described in D377,397 may provide both side-to-side and forward-backward immobility, but its seams between blocks fail to provide adequate radiation resistance, in part due to the substantially large voids found within the blocks but also due to the substantially long horizontal seams found within stacks of blocks.
No existing blocks provide the advantages of the present invention. The art is in need of such improved building blocks.